Empty catacomb contains curious piece (5)
I believe the answer is:
crumb
'piece' is the definition.
(thesaurus)
'empty catacomb contains curious' is the wordplay.
'empty' suggests removing the centre.
'contains' means one lot of letters goes inside another.
'curious' becomes 'rum' (synonyms).
'catacomb' with its middle removed is 'cb'.
'cb' placed around 'rum' is 'CRUMB'.
(Other definitions for crumb that I've seen before include "Small piece of e.g. bread or cake" , "Very small quantity of something, especially food" , "Very little comfort perhaps" , "Small bit (of comfort?)" , "tiny amount" .)